The Pre-CRT Oscilloscope

The same basic principle is still used by better digital scopes to sample periodic waveforms faster than their ADCs can support. This can get you into the TS/s regime on the high end models.

http://cdn.teledynelecroy.com/files/whitepapers/wp_ris_10220...

https://www.tek.com/document/application-note/real-time-vers...

So the "pre-CRT Oscilloscope" is an oscillograph.

When I came in the door in instrumentation work, they'd moved to self-developing photo paper, so we got to use the former darkrooms as additional storage space. CRTs came into use on oscillographs, with the physical galvonometers being replaced by a CRT about half a centimeter tall and 200mm wide displaying dots that were recorded on the photographic paper. They were better at high frequencies, since they didn't have to deal with the physical mass of the galvonometer's rotor (the shaft, coil, and a very small mirror), but since there were a few beams in the CRT multiplexed between signal channels there were compromises in what you could record on one record with a CRT oscillograph, too. Typical galvo o-graphs recorded up to 48 channels on 30cm wide paper, CRTs up to 16 or 32 channels on 20cm paper.

Galvos took a lot of time to set up and calibrate. Adjustments to each one's amplifier, travel range and optical focus, then testing & calibration on each day of use.